low fuel pressure? How do I check it?

What is the fuel pressure when you turn the key on without cranking the engine? Have you replaced the pump or made any repairs? Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check out the diagrams (Below). Please let us know what happens.

Pulled pump and sat it in a bowl of fuel and it sprayed like 3 feet. so i sprayed any dirt in it out and put it back in and it takes 3 cycles turning key off and on before fuel reaches the quick disconnect before rail and injectors. if it sits for even 5 minutes takes another 3 cycles off and on to get fuel to even drizzle out. hooked everything up did a pressure test the needle moves maybe a cm. i was thinking pressure regulator but i can't find one anywhere to even try testing that.

Yep. Your pump is not supplying enough pressure. The regulator is part of the sender/pump and is not serviced separate.

Yea i found a temporary solution, lol. i took a pump motor out of an older Tahoe and junked all but the pieces that hold the pump filter etc., and put the new pump into my casing and back into the tank and it runs good, but if i let off the throttle to suddenly after high speed it just shuts off, but starts immediately again.

Also, i wasn't about to wrestle the tank out again. so my solution was a custom access straight to the pump through the floorboard.

Our 2003 Chevy Tahoe Flex Fuel system doesn't maintain pressure on the fuel line over time and has trouble starting. It rarely starts on first turn of key. We replaced the fuel pump, the fuel filter, the fuel regulator, the throttle body, the crank shaft positioning sensor and still had problems starting the truck. So we decided to check the fuel pressure. We found that after turning the key several times that our fuel pressure was normal and the truck would start but after sitting for an hour or more the pressure would leak down. When we put a gauge on it by the fuel filter the pressure stays consistent over time but when we put the gauge on the fuel rail it goes to zero over time. Is it supposed to do that? If not, what could be causing it? Remember we have already replaced the fuel pump and fuel regulator. The only thing we haven't replaced or checked is the fuel injectors.

At the fuel rail, does the pressure drop more than 5 psi in a minute? If so, after seeing everything you replaced, if it isn't an injector leak, I don't know what it is?

Today we tested the pressure at the fuel rail and it is about 40 psi right after starting it and turning it off which we think is within normal limits for a Flex Fuel system. Then after a couple of minutes of turning it off the pressure went to 45 psi without us doing anything. It is holding steady pressure even after a couple of hours. But now has a new issue, when we start it, it starts running rough and dies. So it seems like the issue is intermittent. It is very frustrating because when it starts running rough it gives a code that there is a communication failure with the crankshaft positioning sensor which we have replaced twice. Also, there is a second code that says ATC failure. What is that about? We are beginning to wonder if this is a PCM problem. Any ideas?

it sounds like the fuel pump is bad.

What is the proper fuel pressure for a 2003 Tahoe

55-62 psi - Here is a guide to help you get the fuel pressure reading.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

Cheers

i have a 2004 chevy tahoe i have changed the plugs factory new i have changed fuel pump twice i have changed all four o2 sensors and fuel filter and mass air flow sensor all new no used i have 42 for fuel pressure unless i accelerate past 3000 rpms then it drops very rapidly almost to 10 to 20 lbs if you just step into it it acts like it is running out of fuel driving me crazy i have gotten the to lean codes on bank i and two so thats what led to changing 02 sensors no improvement i am going insane it is the 5.3 e 85 flex fuel engine oh yeah also replaced fuel pressure regulator new as well please help thanks andy

the fuel pressure should be between 48-54 psi,you either have a another bad fuel pump or a restriction in the fuel feed pipe.these are the only 2 things that can cause low fuel pressure.is the fuel pump aftermarket?if it is I've never had good luck with aftermarket parts.post back with any other questions.

Will run if poor fuel in by hand and will stay running if I keep spraying fuel by hand. getting good pressure to the top on fuel bleed valve on top of the intake. please help.

Good morning,

You need to test the actual pressure to be sure there is enough pressure. You can have fuel to the rail but not enough to have the engine run.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Can you hear the pump run when you turn on the key?

Key On Engine Off .................... 60-66 psi

Roy

Hello and thanks for stopping by. When you say "good pressure," have you actually measured the output with a pressure tester? Or did you just push on the valve and it sprayed out? If you just pushed the valve, then I suggest borrowing a fuel pressure tester from the local auto parts shop and running a pressure test. Pull the fuel pump relay and crank the engine a few times in order to relieve fuel pressure. Then hook up the pressure gauge. Put the relay back in. Turn the key on and see what it reads. These trucks require at least 60 psi to start. Any less will not do it.

If the pressure is just a few pounds short, try replacing your fuel filter. Instructions for that are in the images attached. If it's really low (like 30 psi or less) then you likely need a new pump, which is common to these trucks. In my experience, after 160,000 miles you're on borrowed time with these pumps.

Here's our official guide in checking fuel pressure. It's much better than AllData's guide. https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

So start there and left me know what you find. We'll go from there.

Also, I'm assuming that you have the 5.7L gas engine and not the 6.5L diesel engine. Please let me know if I'm wrong.

I drove to my buddy's house and ran perfectly fine. I went to leave and it wouldn't start. It cranks over really well the battery is still strong . I thought it could be a clogged filter or the pump . I changed the filter and while the filter was disconnected I turned the key on and the pump made a big puddle of fuel. Could it still be the pump? I'm going back today to check for spark hopefully that pans out.

Hi,

Yes, just because a pump is not able to start the vehicle does not mean it cannot pump any fuel. The best way to test a fuel pump is to measure your fuel pressure while cranking. Just because it can deliver some fuel does not mean it can deliver the proper amount of fuel.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know what you find and we can go from there. Thanks

why do i have to spray my truck with ether to get it to start and then it shuts off when i put it into gear.and where is the fuel pressure regulator?

It sounds like a fuel related problem. The regulator is on the fuel rail. I recommend checking the fuel pressure to see how much there is.

Here is a how to for checking.

https://www.2carpros.com/how_to/how_to_check_fuel_pressure.htm

Let me know what you find.

Joe

how much fuel pressure is need while run siting still how low is to low.

56 to 62 PSI... Below 56 is where you will start having problems. Also, make sure there isn't a problem with the regulator. Here is a how to video that explains how to check it. I hope it helps.

https://www.2carpros.com/dia/test_fuel_pressure.htm

Let me know if you have other questions.

Joe

1. What should the fuel pressure be when the key is turned on, motor not running?
2. What should the fuel pressure be with the motor running?
3. Does the fuel pump stop running with the key in the on position engine not running after it builds pressure in the system?

I have no codes, no misfires show on hand held scanner, truck sputters going down the road under no load, when you accelerate it runs fine starts hard once and a while.

Okay, there is no key on engine off specs but it should build up enough pressure to start. Yes the fuel pump will only run for about three seconds with the key on engine off but it should run all the time with engine running. With that the fuel pressure should be 60-66 psi and needs to have full pressure to start. With you problems I must ask how old is the fuel filter?

New fuel filter a week ago, new cap, rotor, wires, and spark plugs. I have 62 to 64 PSI with key on and when I start the motor the fuel pressure drops to 56 to 57 PSI and stays there at a idle.

Okay, the fuel pressure is low when it is running. So check the vacuum line going to the pressure regulator make sure it is good. If all that is good then unplug the pressure regulator and see what the pressure does. It really needs to be in that 60-66 psi range. get back to me with what you find.

Where is the pressure regulator on this vehicle?
with 5.7, is it in the plenum,? it is not visible to me and I do not see the vacuum line either.

Yes, it is under the upper plenum and it does not have a vacuum line to it as it is set by spring pressure internally. So if the fuel pressure is low this is more then likely the problem. Also, these injection systems like to crack the fuel lines that connect to the injector unit and leak. So I would replace the regulator and check those lines for any signs of leaking there is a repair kit for them at most parts stores if it does look like it cracked. With out the fuel pressure up to full pressure there is not much more we can do for tests as this will affect them. Let me know what you do and how it goes.

We replaced the fuel pressure regulator, it was washed out and clean right under the regulator like it had been leaking, flushed injection system,then had to clear the codes because of misfires, took truck out for a drive and it still acted up. Put scanner on it and it all looked good except for -14 on cam timing. Took it to my local GM dealer and they reset the timing and said the truck was fine. But now when I go up a hill under load it pings and knocks then goes away. any ideas?

Check the knock sensor. make sure it is plugged in and working.

I just traded for a 1997 two door Yukon with a Vortex 5.7. it will not start unless you put a little gas in the breather. I tested pressure it is like at 40 psi when you turn key on fuel pump runs is it just not strong enough to start it?

Dpierce.

The cam retard at -17 is not good. The dealer change the position of the distributor to get the 0 reading that the cam sensor requires.

Doing that s compensation for a worn timing chain. That is why you have pinging. Most likely you will need to replace a worn timing chain and then have the cam retard reset.

Roy